[Topoisomerase I from human placenta. Functional activity of products of expression of cloned cDNA fragments].

Immunoscreening of the human placenta cDNA-library in the expression vector lambda gt11 using non-isotope detection based on the avidin-biotin system allowed to identify a number of clones encoding human topoisomerase I. The fusion protein from an extract of Escherichia coli cells infected with the recombinant phage lambda gt11 interacts with the monoclonal antibody raised against topoisomerase I from calf thymus; the dissociation constant being 5.7.10(-8) M. The restricted DNA fragments coding for the topoisomerase polypeptide in the composition of the fusion protein were recloned, and expression in the pEX vector was obtained. The functional analysis of the expression products has enabled localization of the epitope of binding the monoclonal antibody. It was demonstrated that the identified fusion protein can be applied for diagnosis of autoimmune diseases.